The present invention relates to a fire-retardant polyolefin composition. More in detail, the present invention relates to a fire-retardant polyolefin composition comprising a polyolefin, an organohalogenous fire retardant and a carbonic acid ester represented by the formula (I): ##STR2## wherein R and R' respectively represent an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aralkyl group or an aryl group, Z represents a residual group of an aliphatic diol, an alicyclic diol, an aromatic diol, a diphenyl ketone diol, or a diphenylsulfone diol and n is 0 or 1.
Since polyolefins are high in strength, excellent in electrical insulation and easily subjected to molding, polyolefins are used in a broad field as constructional materials, materials for electrical equipments, etc., however, they have a defect that they are combustible and easy to catch fire.
Accordingly, in order to obtain fire-retardant polyolefins, methods of adding various halogen compounds, particularly an organohalogen compound as a fire retardant to polyolefins have been proposed, however, any fire retardant which is excellent in fire retardance and low in bleeding has not been supplied. For instance, as a fire retardant for polyolefin, etherified tetrabromobisphenol A has been proposed (refer to Japanese Patent Publication No. 45-9645(1970)). However, although etherified tetrabromobisphenol A is low in bleeding as compared with other fire retardant, the bleeding is caused in the case of adding a large amount thereof to polyolefin in order to increase a fire retardant property. In order to improve such a situation, a method of using chlorinated polyethylene together with etherified tetrabromobisphenol A has been proposed (refer to Japanese Patent Publication No. 50-23064(1975)), however, chlorinated polyethylene is low in fire retardance and is thermally deteriorated at thermal molding, thereby resulting in bleeding and coloration of the molded articles.
Further, the polyolefin composition containing a derivative of tetrahalogenodiphenylsulfone as the fire retardant (refer to Japanese Patent Publication No. 50-35103(1975)) is poor in the workability on molding and is still insufficient in bleed-preventing effect, and the polypropylene composition containing etherified tetrabromobisphenol A and tetrabromobisphenol A polycarbonate (refer to Japanese Patent Publication No. 55-41698(1980)) causes bleeding in the case of adding a large amount of the above fire retardant to increase a fire retardant property. Also the polypropylene composition containing etherified tetrabromobisphenol A, etherified tetrabromobisphenol S and/or tris(2,3-dibromopropyl)isocyanurate (refer to Japanese Patent Application Laying-Open (KOKAI) No. 57-73032 (1982)) is still insufficient in bleed-preventing effect.
In the case where the prevention of bleeding is insufficient in the composition, the fire retardant bleeds to the surface of the molded article, thereby causing blooms. The molded articles having the blooms of the fire retardant become to be inferior in the fire retardance thereof. It is not only unfavorable from the viewpoint of the physical properties of the molded articles but also the appearance of the molded articles is deteriorated. Namely, the blooming remarkably reduces the commercial merit of the molded articles by the reason that the blooms scatter from the surface of the molded articles and injure the human body.
It is considered that the bleeding is caused by the separation of the fire retardant and polyolefin to each other due to the poor compatibility of the two materials.
As a result of the present inventors' studies based on the idea that a component compatible to both organohalogenous fire retardant and polyolefin may be able to prevent the bleeding, the present inventors have found that a carbonic acid ester represented by the formula (I): ##STR3## wherein R and R' respectively represent an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aralkyl group or an aryl group; Z represents a residual group of an aliphatic diol, an alicyclic diol, an aromatic diol, a diphenyl ketone diol or a diphenylsulfone diol and n represents 0 or 1, is compatible to both polyolefin and organohalogenous fire retardant, and the addition of the carbonic acid ester represented by the formula (I) to the conventional composition comprising polyolefin and an organohalogenous fire retardant remarkably reduces the bleeding of the fire retardant from the molded article without causing the reduction of fire retardance, mechanical strength and electrical characteristics of the molded articles.
On the basis of the findings, the present inventors have attained the present invention.